Enrolment of a Fingerprint Template

1. A fingerprint sensing system comprising: a fingerprint sensor; processing circuitry; and data storage storing instructions executable by said processing circuitry whereby said fingerprint sensing system is operative to: for each of a plurality of consecutive sub-templates of the time sequence: determine that a fingerprint topography of a finger is in proximity to a detection surface of the fingerprint sensor as part of an interaction of the finger with the fingerprint sensor; capture the sub-template of the topography, consecutive to a preceding sub-template in the time sequence; obtain an indication of that the topography remained in proximity to the detection surface during a time period between capturing of the preceding sub-template and the determining that the topography is in proximity to the detection surface, or that the topography did not remain in proximity to the detection surface during said time period; define the interaction as a slide interaction if, according to the obtained indication, the topography remained in proximity to the detection surface, or as a touch interaction if, according to the obtained indication, the topography did not remain in proximity to the detection surface during said time period; and based on whether the interaction is defined as a slide interaction or a touch interaction, advance an enrolment progress; and when the enrolment progress is above a predetermined enrolment threshold, enrol the compiled template.

2. An electronic device comprising the fingerprint sensing system of claim 1 .

3. The electronic device of claim 2 , wherein the electronic device is a mobile phone, e.g. a smartphone; a smart card; a tablet computer; a portable computer, e.g. a laptop computer; or a stationary computer, e.g. a desktop computer, a server or a mainframe computer.

4. A method performed in an electronic device comprising a fingerprint sensing system comprising a fingerprint sensor for enrolling a fingerprint template compiled from a time sequence of sub-templates, the method comprising, by means of the fingerprint sensing system: for each of a plurality of consecutive sub-templates of the time sequence: determining that a fingerprint topography of a finger is in proximity to a detection surface of the fingerprint sensor as part of an interaction of the finger with the fingerprint sensor; extracting the sub-template from a captured image of the topography, which sub-template is consecutive to a preceding sub-template in the time sequence; obtaining an indication about whether or not the topography remained in proximity to the detection surface during a time period between capturing an image from which the preceding sub-template was extracted and the determining that the topography is in proximity to the detection surface; defining the interaction as a slide interaction if, according to the obtained indication, the topography remained in proximity to the detection surface, or as a touch interaction if, according to the obtained indication, the topography did not remain in proximity to the detection surface during said time period; and based on whether the interaction is defined as a slide interaction or a touch interaction, advancing an enrolment progress; and when the enrolment progress is above a predetermined enrolment threshold, enrolling the compiled template.

5. The method of claim 4 , wherein the enrolment progress is advanced with a higher value if the interaction is defined as a touch interaction than if the interaction is defined as a slide Interaction.

6. The method of claim 4 , wherein for at least one of the plurality of consecutive sub-templates the interaction is defined as a slide interaction, and wherein for at least one other of the plurality of consecutive sub-templates the interaction is defined as a touch interaction.

7. The method of claim 4 , wherein the extracting of the sub-template comprises: capturing the image of the topography; comparing features of the captured image with corresponding features of the image of the preceding sub-template to obtain a value of translation there between; and determining that the translation value is above a predetermined translation threshold.

8. The method of claim 7 , wherein the translation threshold is dependent on whether the interaction is defined as a slide interaction or a touch interaction.

9. The method of claim 4 , wherein each of the sub-templates of the time sequence covers an area of the topography corresponding to an area of the detection surface which is smaller than an area of the topography covered by the enrolled template.

10. The method of claim 9 , wherein the area of the detection surface is at most 20 mm 2 .

11. The method of claim 10 , wherein the area of the detection surface is less than 15 mm 2 .

12. The method of claim 4 , wherein the fingerprint sensor comprises a two-dimensional array of fingerprint sensing elements arranged beneath the detection surface.

13. A non-transitory computer-readable storage medium having a plurality of instructions stored thereon, which, when executed by the one or more processors, cause the one or more processors to perform the method of claim 4 .